Si3453
12 Rev. 1.3
4. Functional Description
Integrating four independent high-voltage PSE port interfaces, the Si3453 high-voltage port controller enables
extremely flexible solutions for virtually any PoE or PoE+ PSE application. The Si3453 provides all of the high-
voltage Power over Ethernet PSE functions.
Each port of the Si3453 integrates all high-voltage PSE controller functions needed for a quad-port PoE design,
including the power MOSFET, efficient current-sensing circuitry, transient voltage surge suppressor, and multiple
detect and disconnect circuits. When the dc disconnect sensing method is selected, the external BOM is typically
only a single filter capacitor on each high-voltage port.
When a PD device has been properly detected and classified, the port is powered by a –54 V nominal supply with
continuous monitoring of voltage and current for feedback to the host system.
In addition to the required IEEE features, the Si3453 includes many additional features:
Per port current / voltage monitoring and measurement
Support for 1-Event and 2-Event classification algorithms
Start up in shutdown or auto mode
Alternative A (typically used for endpoint systems) or Alternative B (typically used for midspan systems)
detection timing
4.1. Detection
The Si3453 has per-port signature detection that satisfies the IEEE Std 802.3™-2005 specifications. However, by
utilizing a 3-point voltage-forced detection method, the Si3453 yields robust recognition of valid and invalid
powered device (PD) signatures, properly identifying signatures often mischaracterized by other detection
techniques.
Figure 4. PSE Sequencing (3-Point Detection followed by 2-Event Classification and Powerup)
Vport Relative to GND
The detection circuitry performs the function of setting the output voltage on any channel to the proper value for
detection or classification and then measuring the resulting line current.
A typical detection cycle consists of applying 4 V, then 8 V, then 4 V again with the current limit set to 3 mA. The
current is measured after an appropriate settling time. For a valid PD, the detection signature must be compliant
with the detection voltage both increasing and decreasing.
3 point
detection
2 event
classification
Port powerup
